Increased risk of wet summer in the northeast

The Bureau's summer rainfall outlook shows that there's an increased
likelihood of above average seasonal falls in northeast Queensland.
Elsewhere in the State, the odds are neutral, that is, they're
close to 50:50.
This outlook is largely the result of recent temperature patterns
and trends in the Indian Ocean.

For the December to February period, the chances of above median
rainfall are between 60 and 65% over a region in
northeast Queensland within about 300km of Townsville (see map).
So with climate patterns like the current,
about 6 seasons out of 10 are expected to be wetter than average in
this part of Queensland, with about 4 out of 10 being drier.

Outlook confidence is related to the influence of Pacific and Indian
Ocean temperatures on seasonal rainfall. During summer,
history shows this influence to be moderate in southern and eastern Queensland,
but weak to very weak in the central and western parts of the state (see background information).

The tropical Indian Ocean has been cooling strongly over recent months and
temperatures there are currently close to average.
The Pacific on the other hand, is generally
warmer than average, particularly in the west. For more detail
see the El Niño Wrap-Up.
The recent temperature changes in the Indian Ocean are the dominant
influence on the overall pattern of probabilities.

October's value of the Southern Oscillation Index
(SOI) was 2, the same as that recorded in September and August.
The approximate SOI for the 30 days ending 11th November was 3.

Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.

More information on this outlook is available
from 9.00am to 5.00pm (EST)
Monday to Friday by contacting the
Climate and Consultancy section in the Bureau's
Brisbane Office: (07) 3239 8669 or (07) 3239 8666.

THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 16th DECEMBER 2003.

Probability outlooks should not be used as if they were categorical forecasts.
More on probabilities is contained in the booklet
The Seasonal Climate Outlook - What it is and how to use it,
available from the National Climate Centre.
These outlooks should be used as a tool in risk management
and decision making.
The benefits accrue from long-term use, say over 10 years.
At any given time, the probabilities may seem inaccurate,
but taken over several years, the advantages of taking account
of the risks should outweigh the disadvantages.
For more information on the use of probabilities,
farmers could contact their local departments of agriculture or primary industry.

Model Consistency and Outlook Confidence:
Strong consistency means that tests of the model on historical
data show a high correlation between the most likely
outlook category (above/below median)
and the verifying observation (above/below median). In this
situation relatively high confidence can be placed in the
outlook probabilities.
Low consistency means the historical relationship, and
therefore outlook confidence, is weak.
In the places and seasons where the outlooks are most skilful,
the category of the eventual outcome (above or below median)
is consistent with the category favoured in the outlook
about 75% of the time.
In the least skilful areas,
the outlooks perform no better than random chance or guessing.
The rainfall outlooks perform best in eastern and
northern Australia between July and January,
but are less useful in autumn and in the west of the continent.
The skill at predicting seasonal maximum temperature peaks in
early winter and drops off marginally during the second half of the year.
The lowest point in skill occurs in early autumn.
The skill at predicting seasonal minimum temperature peaks in
late autumn and again in mid-spring.
There are also two distinct periods when the skill is lowest
- namely late summer and mid-winter.
However, it must always be remembered that the outlooks
are statements of chance or risk.
For example, if you were told there was a 50:50 chance
of a horse winning a race but it ran second,
the original assessment of a 50:50 chance could still have been correct.

The Southern Oscillation Index (SOI) is calculated using the
barometric pressure difference between Tahiti and Darwin.
The SOI is one indicator of the stage of El Niño or La Niña
events in the tropical Pacific Ocean.
It is best considered in conjunction with sea-surface temperatures,
which form the basis of the outlooks.
A moderate to strongly negative SOI (persistently below 10) is
usually characteristic of El Niño, which is often associated with below
average rainfall over eastern Australia, and a weaker than normal monsoon
in the north. A moderate to strongly positive SOI (persistently above +10)
is usually characteristic of La Niña, which is often associated with
above average rainfall over parts of tropical and eastern Australia,
and an earlier than normal start to the northern monsoon season.
The Australian impacts of 23 El Niño events since 1900 are summarized
on the Bureau's web site
(www.bom.gov.au/climate/enso/).